1. Field of the Invention
This invention relates to a rotary shaft for a rotary switch and more particularly it relates to a channel changing shaft for a television tuner or channel selector, said rotary shaft being molded of a synthetic resin.
2. Description of the Prior Art
A rotary type television tuner, such as one shown at 100 in FIG. 1, has already been widely known. As known in the art, the television tuner 100 includes a channel changing shaft 10. A detent rotor 40 for intermittent positioning, and a changing plate 50 are fixedly mounted on the shaft 10 so that they can be rotated integrally with the shaft 10. The channel changing shaft 10 is inserted in holes in switching plates 60 and 70 which have tuning elements attached thereto and are fixed to a chassis 30. The chassis 30 is made up of chassis component plates and accommodates the detent rotor 40, changing plate 50 and switching plates 60 and 70, with a presetting mechanism 31 provided at one end thereof. The presetting mechanism 31 has a fine tuning shaft 20 connected thereto. The fine tuning shaft 20 is rotatably mounted on the channel changing shaft 10 to provide for fine tuning which is effected by rotating the same.
The channel changing shaft 10, which is circular in cross-section, is formed with a flat portion 11 for mounting unillustrated knob thereon, as shown in FIG. 2. The rotation of the knob mounted on the front end of the shaft 10 causes the rotation of the changing plate 50, whereby of the terminals 51 and 52 which are formed on the outer periphery of the changing plate 50, a selected pair of terminals are clamped by contact clips 53 and 54, whereby a change to a desired channel is effected.
Conventionally, the channel changing shaft 10 of such rotary type television tuner 100 has been made of iron or other metals. However, metals are difficult to work with and working them into complicated shapes, especially a flanged part for turning the changing plate 50, is difficult. Further, since such working is performed by turning the shaft down in a lathe, it entails a materials loss, and in the case of iron, a surface treatment, such as plating, for rust proofing is required. Which adds to the cost. In particular, when the shaft 10 is assembled to the television tuner, it is necessary to provide accessories such as grounding springs used to assure that the chassis 30 and shaft 10 are at the same potential (ground potential) and end insulators required by safety standards to prevent the exposure of metal at the knob.
It may be easily thought of to employ synthetic resins in producing the channel changing shaft. However, a simple changeover of materials from metal to synthetic resin would not be sufficient. In the case of a television tuner as contrasted with communication equipment, for example, the knob is subject to rough manipulation. In such case, there would arise a new problem of such synthetic resin shaft being broken adjacent the knob, which is not a problem with the metal shaft.